Studies on the structure, ligand specificity and mechanism of activation of the nicotinic acetylcholine receptors will be continued. Our approach is directed to understanding how the natural transmitter and other agonists elicit a change in conductance upon association with the receptor and how pharmacologic antagonists render the receptor nonfunctional. Many of the antagonists studied are employed in clinical practice to produce muscle relaxation. Our approach combines the pharmacologic analyses of ligand occupation and the functional states of the receptor with physical, chemical, and biochemical studies on receptor structure. The physical chemical investigations rely heavily on fluorescence spectroscopy to examine conformational changes attended to ligand binding and intersite distances on the receptor. Several fluorescent antagonists have been synthesized and we hope to delineate the sites of action of competitive antagonists and noncompetitive agents by analysis of fluorescence energy transfer. Studies with isolated receptors will employ the purified receptor from Torpedo. Investigation of the functional states of the receptor is also being pursued in BC3H-1 cells where one can simultaneously measure agonist elicited permeability changes and ligand occupation of the receptor. The structural studies will rely on site specific labeling of the receptor and identification of the residues on the receptor involved. To this end, we are unraveling the action of lophotoxin which reacts covalently with this receptor and enjoys a specificity for one of the two Alpha subunits.